1. Technical Field
The present invention relates to a display device and, more particularly, to a horizontal size regulation circuit of a display device which regulates the voltage applied to a deflection coil of a horizontal output circuit in a horizontal deflection circuit of the display device, using the switching operation of an active element, to maintain a specific horizontal size.
2. Related Art
Generally, a display device such as a CRT type of monitor is a peripheral device which processes information data received from an information data system such as a computer system and provides a visual display of the processed information data on a screen. In all display devices, a video card which is installed in the information data system, outputs a video signal in accordance with vertical and horizontal synchronous signals for a visual display. The vertical and horizontal synchronous signals exhibit different frequencies according to different operation modes of the video card. When the operation mode of the video card in the computer system is changed to display a desired signal on the screen of the display device, the display device discriminates the changed operation mode on the basis of the frequencies of the vertical and horizontal synchronous signals from the video card, and provides a visual display in accordance with the discriminated operation mode.
A conventional display device generally includes a microprocessor which receives the vertical and horizontal synchronous signals from the video card to control the visual display of information data on a screen, and vertical and horizontal deflection circuits which respectively receive the vertical and horizontal synchronous signals to perform vertical and horizontal deflection, such that an electron beam generated by an electron gun of a cathode ray tube (CRT) is deflected in a regular sequence from an upper left portion to a lower right portion of the CRT by way of a deflection yoke in order to form an image. A high voltage generating circuit, such as that disclosed in U.S. Pat. No. 5,438,245 for High Voltage Generating Circuit issued to Kii et al., is included to stably supply a high voltage to the anode of the CRT in response to a flyback pulse generated by the horizontal deflection circuit. Video amplifiers then serve to amplify an RGB video signal transmitted from the video card to a level of approximately 40-60 Vpp for providing energy to each pixel.
In such a display device, deflection circuits perform either an electrostatic deflection using an electric field or an electromagnetic deflection using a magnetic field. As a result, an image is formed on the CRT monitor from the electron beam projected onto a fluorescent surface thereof by outputting a sawtooth current waveform to horizontal and vertical coils. An example of such a horizontal deflection circuit is disclosed in U.S. Pat. No. 4,263,615 for Horizontal Drive Circuit For Video Display issued to Steinmetz et al. Generally, the horizontal deflection circuit includes a horizontal drive circuit and a horizontal deflection output circuit, for generating an output horizontal deflection signal outputted to a deflection yoke mounted on the CRT. The horizontal deflection output circuit typically includes a transformer for amplifying a horizontal drive signal and a horizontal output transistor which operates in response to an output of the transformer to generate an output horizontal deflection signal.
A contemporary horizontal deflection circuit, as I have observed however, often fails to effectively regulate the horizontal voltage supplied to the deflection coil of the horizontal output circuit. As a result, errors in the horizontal size regulation may be severe, resulting in deterioration of the stability of the circuit and distortion of the displayed image.